STUDY ON SEDIMENTARY FACIES OF THE UPPER SHA-4-SHA-3 MEMBER OF SHAHEJIE FORMATION (PALAEOGENE) IN THE NORTHEASTERN OF ZHANHUA SAG

Zhanhua sag is a sub-sag in the northeastern Jiyang depression. During the late Sha-4 (Es4) - Sha-3 (Es3) epoch (the Fourth - Third Member of Shahejie Formation, Palaeogene), Zhanhua sag was developed into a fault-sag basin steep in the north and gentle in the south. During the late Es4 epoch, the northeastern Zhanhua sag was consisted of two sub-sags, one was located in the east and the other in the west. The deposits were mainly fan-delta, gypsum-salt lake and lacustrine facies, which generally distributed in annuluses. In the Es3 epoch, the deposits were mainly semi-deep-deep lake facies, fan-delta and sublacustrine fan facies. The semi-deep-deep lake facies was the most developed deposits and distributed a little more further to the north of the basin. The shore-shallow lake facies were mainly distributed on the north edges of the bulges in the south. The fan-delta facies were mainly distributed on the edges of the bulges. There were two types of sublacustrine fan facies, i.e., normal type and trough type. The normal sublacustrine fan facies were developed on the north edge of Gudao bulge in the south part, and the trough ones were situated on the slope zones on the steep banks of Yihezhuang bulge and Chengzikou bulge. During the middle of Es3 epoch, sublacustrine fan facies was greatly developed, two sublacustrine fans which were developed originally on the edges of Chengzikou bulge and Gudao bulge were intersected at the area around well Y115. The shape of resulting sublacustrine fan was protruded towards the west by the obstruction of Guxi fracture belt.